1. Field
Aspects of the present invention generally relate to a track test load device, a track test load system, and a method for testing a constant warning time device.
2. Description of the Related Art
A constant warning time device, also referred to as a grade crossing predictor in the U.S. or a level crossing predictor in the U.K., is an electronic device that is connected to the rails of a railroad track and is configured to detect the presence of an approaching train and determine its speed and distance from a crossing, i.e., a location at which the tracks cross a road, sidewalk or other surface used by moving objects. The constant warning time device will use this information to generate a constant warning time signal for controlling a crossing warning device. A crossing warning device is a device that warns of the approach of a train at a crossing, examples of which include crossing gate arms (e.g., the familiar black and white striped wooden arms often found at highway grade crossings to warn motorists of an approaching train), crossing lights (such as the red flashing lights often found at highway grade crossings in conjunction with the crossing gate arms discussed above), and/or crossing bells or other audio alarm devices. Constant warning time devices are often (but not always) configured to activate the crossing warning device at a fixed time (e.g., 30 seconds) prior to an approaching train arriving at a crossing.
Typical constant warning time devices include a transmitter that transmits a signal over a circuit formed by the track's rails and one or more termination shunts positioned at desired approach distances from the transmitter, a receiver that detects one or more resulting signal characteristics, and a logic circuit such as a microprocessor or hardwired logic that detects the presence of a train and determines its speed and distance from the crossing. The approach distance depends on the maximum allowable speed of a train, the desired warning time, and a safety factor. Preferred embodiments of constant warning time devices generate and transmit a constant current AC signal on said track circuit; constant warning time devices detect a train and determine its distance and speed by measuring impedance changes caused by the train's wheels and axles acting as a shunt across the rails, which effectively shortens the length (and hence lowers the impedance) of the rails in the circuit. Multiple constant warning devices can monitor a given track circuit if each device measures track impedance at a different frequency.
Currently, when testing a failing grade crossing predictor (GCP), a dummy track test load may be used to determine if the problem is in the track or in the GCP. Such a dummy track test load may also be used to set up a GCP system in a lab or shop for testing or training purposes. The dummy track test load is attached to the GCP using ring terminals across an entrance terminal board of the GCP housing, which requires removal of field wiring to allow for the connection of the dummy track test load. Since more than one wire/connector is removed, the Federal Railroad Administration considers that the circuitry has been disarranged and there is a chance that the wires will not be reconnected in the same place as they were removed from which can cause a drastic change in the operation of the GCP system. Furthermore, existing dummy track test load devices provide only limited testing. Thus, there may be a need for a technique for testing a grade crossing predictor which provides easy handling and multiple test options.